Auto merge of #12543 - Xaeroxe:manual-clamp-const, r=xFrednet,GuillaumeGomez

restrict manual_clamp to const case, bring it out of nursery

Implements the plan that I described in #9484 (comment)

This does two things primarily

1. Restrict `manual_clamp` such that it will only trigger if we are able to guarantee that `clamp` won't panic at runtime.
2. Bring `manual_clamp` out of nursery status and move it into the complexity group.

changelog: [`manual_clamp`]: Restrict this lint such that it only triggers if max and min are const, and max is greater than or equal to min. Then bring it out of the nursery group.

Author: bors

clippy_lints/src/manual_clamp.rs

@@ -1,4 +1,5 @@
 use clippy_config::msrvs::{self, Msrv};
+use clippy_utils::consts::{constant, Constant};
 use clippy_utils::diagnostics::{span_lint_and_then, span_lint_hir_and_then};
 use clippy_utils::higher::If;
 use clippy_utils::sugg::Sugg;
@@ -17,6 +18,7 @@ use rustc_middle::ty::Ty;
 use rustc_session::impl_lint_pass;
 use rustc_span::symbol::sym;
 use rustc_span::Span;
+use std::cmp::Ordering;
 use std::ops::Deref;
 
 declare_clippy_lint! {
@@ -26,6 +28,11 @@ declare_clippy_lint! {
     /// ### Why is this bad?
     /// clamp is much shorter, easier to read, and doesn't use any control flow.
     ///
+    /// ### Limitations
+    ///
+    /// This lint will only trigger if max and min are known at compile time, and max is
+    /// greater than min.
+    ///
     /// ### Known issue(s)
     /// If the clamped variable is NaN this suggestion will cause the code to propagate NaN
     /// rather than returning either `max` or `min`.
@@ -80,7 +87,7 @@ declare_clippy_lint! {
     /// ```
     #[clippy::version = "1.66.0"]
     pub MANUAL_CLAMP,
-    nursery,
+    complexity,
     "using a clamp pattern instead of the clamp function"
 }
 impl_lint_pass!(ManualClamp => [MANUAL_CLAMP]);
@@ -103,6 +110,26 @@ struct ClampSuggestion<'tcx> {
     hir_with_ignore_attr: Option<HirId>,
 }
 
+impl<'tcx> ClampSuggestion<'tcx> {
+    /// This function will return true if and only if you can demonstrate at compile time that min
+    /// is less than max.
+    fn min_less_than_max(&self, cx: &LateContext<'tcx>) -> bool {
+        let max_type = cx.typeck_results().expr_ty(self.params.max);
+        let min_type = cx.typeck_results().expr_ty(self.params.min);
+        if max_type != min_type {
+            return false;
+        }
+        if let Some(max) = constant(cx, cx.typeck_results(), self.params.max)
+            && let Some(min) = constant(cx, cx.typeck_results(), self.params.min)
+            && let Some(ord) = Constant::partial_cmp(cx.tcx, max_type, &min, &max)
+        {
+            ord != Ordering::Greater
+        } else {
+            false
+        }
+    }
+}
+
 #[derive(Debug)]
 struct InputMinMax<'tcx> {
     input: &'tcx Expr<'tcx>,
@@ -123,7 +150,7 @@ impl<'tcx> LateLintPass<'tcx> for ManualClamp {
                 .or_else(|| is_match_pattern(cx, expr))
                 .or_else(|| is_if_elseif_pattern(cx, expr));
             if let Some(suggestion) = suggestion {
-                emit_suggestion(cx, &suggestion);
+                maybe_emit_suggestion(cx, &suggestion);
             }
         }
     }
@@ -133,13 +160,16 @@ impl<'tcx> LateLintPass<'tcx> for ManualClamp {
             return;
         }
         for suggestion in is_two_if_pattern(cx, block) {
-            emit_suggestion(cx, &suggestion);
+            maybe_emit_suggestion(cx, &suggestion);
         }
     }
     extract_msrv_attr!(LateContext);
 }
 
-fn emit_suggestion<'tcx>(cx: &LateContext<'tcx>, suggestion: &ClampSuggestion<'tcx>) {
+fn maybe_emit_suggestion<'tcx>(cx: &LateContext<'tcx>, suggestion: &ClampSuggestion<'tcx>) {
+    if !suggestion.min_less_than_max(cx) {
+        return;
+    }
     let ClampSuggestion {
         params: InputMinMax {
             input,